Wire live Prism node injection into JSON-parsed AST (herb-embedded-gu7)

[jleo3]

Summary

• ResultEnvelope.parse computes Prism.dump(Herb.extract_ruby(source)).bytes (a JSON-safe Integer array) and injects it onto the root parsed value's prism_node key when prism_program is requested, instead of forwarding that flag into Herb.parse itself.
• This makes the prism_program-backed rules (erb-no-debug-output, erb-no-instance-variables-in-partials) produce real diagnostics through Bridge#lint.
• prism_nodes/prism_nodes_deep (per-ERBContentNode injection, used by the other 10 prism-dependent rules) remains out of scope, documented in CHARTER.md.

Acceptance criteria

• At least one of the 15 prism-dependent rules produces a real, correct diagnostic through Bridge#lint — new spec in spec/bridge_lint_spec.rb lints <div><%= @foo %></div> against erb-no-instance-variables-in-partials for a partial-named file and asserts a real offense (plus a negative control for a non-partial filename).
• The mechanism does not reintroduce the JSON::GeneratorError bug — FORWARDABLE_OPTIONS still excludes prism_program/prism_nodes/prism_nodes_deep from ever reaching Herb.parse; the injected bytes are computed separately as a plain Integer array, never a raw ASCII-8BIT string.
• A note documents which of the 15 prism-dependent rules are covered and which remain out of scope — new sub-bullet in CHARTER.md's Shape decisions, naming all 12 rules that declare a Prism mode via parserOptions and the reason the other 10 (prism_nodes) aren't covered yet.

Test plan

• bundle exec rake (RuboCop + full RSpec suite) passes locally, including the two new specs.
• Manually verified erb-no-debug-output and erb-no-instance-variables-in-partials both produce real diagnostics through Bridge#lint against hand-built fixtures.

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